This invention relates to a dehydrogenation process for producing indene and styrene, and more particularly, to a process of preparing indene and styrene from readily available butadiene and cyclopentadiene or dicyclopentadiene.
Indene is present in low concentrations (e.g., 12-16%) in ethylene or gas oil cracking co-products, but it has been difficult to recover the indene in satisfactory yields and purity from these low concentration sources. Indene is a desirable raw material for preparing superior heat-resistant polymers.
Styrene is generally produced from the catalytic dehydrogenation of ethylbenzene. For example, U.S. Pat. No. 3,933,932 describes the conversion of ethylbenzene to styrene by an oxydehydrogenation reaction utilizing catalysts such as lanthanum phosphate, lanthanum pyrophosphate or rare earth phosphates containing a major portion of lanthanum phosphates or pyrophosphates. Styrene monomer can be polymerized by exposure to light, heat or peroxide catalysts. Homopolymers and copolymers of styrene are widely used thermoplastic materials. It is, accordingly, desirable to provide additional sources of styrene from readily available materials.
Butadiene is a gas obtained from cracking of petroleum, from coal tar benzene and from acetylene. Butadiene, as well as cyclopentadiene and dicyclopentadiene, are readily available and relatively inexpensive chemicals.
The invention of this application is directed particularly to the preparation of indene and styrene from a mixture of tetrahydroindene and vinylcyclohexene. Mixtures of tetrahydroindene and vinylcyclohexene can be recovered from the reaction products formed in Diels-Alder reactions of butadiene with cyclopentadiene or its dimer, dicyclopentadiene. A considerable amount of research has been conducted and published on this reaction, and various suggestions have been made for optimizing production of the various co-products such as tetrahydroindene and vinylcyclohexene.
The dehydrogenation of indene precursers such as tetrahydroindene into indene has been described in the art and generally is conducted in the presence of dehydrogenation promoting catalysts. In U.S. Pat. No. 4,143,082, the dehydrogenation of indene precursers into indene is accomplished by contacting the indene precurser in the presence of an oxygen donor with a phosphate catalyst at elevated temperature. These catalysts, described more fully in the patent, are salts of one of the phosphoric acids. Other types of dehydrogenation catalyst have been described in the literature, and such compounds include the metal oxides, metal salts such as the halides, phosphates, sulfates, molybdates, tungstates, etc. Generally, the catalysts are characterized as compounds containing a metal having a polyoxidation state, that is, a metal having at least two oxidation states in addition to the zero state. Examples of useful polyoxidation state metals include Ti, V, Cr, Mn, Co, Ni, Cu, Nb, Mo, Ru, etc.
In addition to the use of polyoxidative state metals, oxidation catalysts also may be combined with one or more monooxidation state metals which act as promoters, initiators, stabilizers and the like. The single oxidation state metal or metal compounds include the alkali metals, and polyvalent metals such as magnesium, aluminum, calcium, scandium, zinc, etc. The use of cobalt and molybdenum oxides promoted with potassium oxide in dehydrogenating indane to indene is reported in Czech Pat. No. 135,251. The catalyst bed contained 3% CoO, 10% MoO.sub.3 and 0.3% K.sub.2 O. A review of the various catalysts useful in oxidative dehydrogenation of organic compounds is found in U.S. Pat. No. 3,925,498. U.S. Pat. 3,887,631 describes the oxidative dehydrogenation of hydrocarbons such as butene and ethylhexane by use of a catalyst consisting essentially of the oxides of molybdenum, cobalt and boron.